Patent application PCT/EP2008/057009 describes a reversible variable transmission comprising so-called planetary variators, overcoming the limitations and disadvantages of actual car transmissions, such as manual transmission (MT), automatic transmission (AT), double clutch transmission (DCT), continuously variable transmission (CVT) and hydrostatic drive (HSD).
According to the patent application mentioned above, a combination of one or more planetary variators in different variable transmission layouts may be used. The planetary variators function as subsystems for variable or reversible transmissions, able to vary continuously the transmission ratio, and consisting of a ring wheel, two or more planets mounted around a central shaft and a sun wheel, so that the ring wheel, the central shaft and the sun wheel form an interface with other transmission components. The planets consist of a planet wheel with basically a conical rolling surface, preferably hardened or coated to transmit tractional and compressive forces, mounted freely rotational around a planet fork by means of radial and axial bearings or bushings and that the virtual top of the mentioned cone coincides with the intersection of the axis of the central shaft with the axis of the hinge of the planet. Each planet fork of a planetary variator can rotate freely around a hinge joint of which the axis is perpendicular on the central shaft axis and parallel to the planet wheel plane and that each planet fork and each planet wheel is designed not to interfere with each other for all applicable inclination angles between the planet axis and the central shaft axis. The ring wheel, planets and sun wheel are squeezed against each other so that the rolling surfaces are in contact with each other and that the contact pressures are high enough to transmit the required torque. The central shaft is moved axially with a defined speed in relation to the squeezing force and transmitted torque, in order to change the transmission ratio and the shape of the rolling surfaces of the planet wheels, which is basically conical, deviates slightly from this theoretical shape in a convex way in order to optimize the contact pressure distribution.
Considering reversible variable transmission of patent application PCT/EP2008/057009, comprising a primary and a secondary planetary variator, the ring wheel of the primary planetary variator is connected to the housing so that it cannot rotate but can move axially by a preload force compressing rolling contacts of both planetary variators. The central shafts of both planetary variators are combined into one main shaft and rotationally connected to the transmission input shaft and axially movable by a steering force in both senses, while the input shaft does not move axially. The sun wheel of the primary planetary variator is connected to the ring wheel of the secondary planetary variator so that the combined sun-ring wheel can rotate around the central axis of the transmission. The sun wheel of the secondary planetary variator is connected to the output shaft of the transmission and that the reaction force of the preload force is transferred to the housing over an axial bearing.
The relative dimensions of the ring wheel, sun wheel and planets are preferably chosen appropriate for a car application, meaning that the highest speed ratio is so high that the engine can deliver its power nearly always at its best efficiency point, but also meaning that the highest speed ratio in reverse is high enough to drive the car with moderate engine speed and low noise in reverse. By moving the main shaft of the transmission, the transmission ratio varies continuously between the highest speed ratio in forward over standstill to the highest transmission ratio in reverse.
The normal force on each rolling contact is created by one preload force, acting from the housing on the not rotating primary ring wheel and the reaction force is transferred over one bearing from the secondary sun wheel to the housing. The net steering forces for defining the position of the main shaft and thus also for defining the transmission ratio, are created by one force in one of both senses and acting from the input shaft to the main shaft, both rotating with the same speed, and that the reaction force is transferred over bearings from the input shaft to the housing.
The preload force as explained above is created by one or more piston and cylinder system(s) between housing and primary ring wheel and activated by a single pneumatic or hydraulic pressure or created by a mechanical preload system, where this mechanical system can also be used as parking brake when the transmission is put in zero speed ratio. The steering pressure is created by a hydraulic or pneumatic piston cylinder system, able to work in both senses, integrated in the input shaft and main shaft. The hydraulic or pneumatic pressure to create the steering pressure is sealed between the stationary housing and the rotating input shaft by piston rings or seals designed to seal parts rotating at different rotational speeds.
The reversible variable transmission of patent application PCT/EP2008/057009 as referred to above, also provides a hydraulic system and application software program, intended to control reversible variable transmission with a hydraulic valve in a car, truck or other on-highway or off-highway vehicle.
The transmission interior, where the rolling contacts are moving, is filled with an inert gas, or normal air and a splashing fluid for cooling and lubrication, or a gas with a mist of a coolant and said interior is sealed from the lube oil for the bearings and from the exterior of the transmission. Multiple options of lubrication flow for the bearings or bushings inside the planets are given with the reversible variable transmission of patent application PCT/EP2008/057009.
The reversible variable transmission provides the user to transmit power at variable speeds in a car, truck, bus, off-road vehicle, mowing machine, wind turbine, telescopic boom handler, lift truck or any other industrial application in which power needs to be transmitted at variable speeds.
The configuration of the reversible variable transmission system contains however further improvement potential in terms of power density: with the same outer dimensions more power can be transmitted. Within the same transmission size and with the same traction coefficient, more power is transferred by applying higher normal forces on the traction wheels and by using the transmission closer to the traction limit. The underlying invention discloses several design modifications resulting in a higher power density.